Such a key switch is used, for example, in automated production plants or devices with possibilities for intervention for manual operation or control of processes which are activated via electrical switching elements.
Further applications are conceivable in technical facilities in which unwanted or unauthorized activation of an operating state of the facility, which includes certain hazards, must be prevented.
In the so-called set up mode of an automated production plant or device, for example, so-called key switches are preferably used today which can only be operated by the key in position of the authorized person. Using key switches with key monitoring makes it possible both to prevent the key from being forgotten in the key switch and unauthorized switching in an unsecured operation of the production plant or device since, similarly to the removal, the insertion of the key can also be detected.
The current state of the art teaches key monitoring which is implemented, for example, by use of a micro-switch which is mounted in the key channel. In known key switches with key monitoring, an ejection or dropping out of the key is provided when the micro-switch is not yet operated. It is a disadvantage that the micro-switches used in most cases do not have mandatory contact opening and are mechanically sensitive to soiling and foreign bodies. Furthermore, the assembly of the micro-switch solution is very expensive and has a relatively short service life.
From EP 0 412 374 B1, a key switch is known which only enables an altered operating state of a technical facility to be activated when the key is removed. By way of the key inserted by a minimum depth, a switching contact is operated in a micro-switch located in the key channel of the key switch. In this arrangement, the key is held in the key channel without external support once the minimum depth has been reached.
For reasons of security and authorization it is desirable to eject the key out of the key channel when the key switch is not operated. For this purpose, the current state of the art provides mechanisms which are based on a restoration effect on the key. The restoration effect can act permanently on the key and be blocked in the operated position. This ensures that, when the key switch is operated, the key remains in the key channel whereas the key can be automatically ejected in the non-operated position.
From DE 88 00 701.4 U1, a control switch is known which ensures, by way of a return spring, that after the key has been turned into an off position and released, it is pressed out of the switch.
Furthermore, a type of key monitoring must be called disadvantageous which only triggers an operation of a switching element for detection of the key close to the end position of the key. This is because, in this arrangement, the key is in the vicinity of the initial position in the key channel without being detected.
From U.S. Pat. No. 6,969,810 B1, a key switch is known which performs a detection of the key close to the end position and prevents the key from remaining in the key channel by way of a spring mechanism.